U.S. patent number 11,084,283 [Application Number 16/676,070] was granted by the patent office on 2021-08-10 for methods of forming and using fluid ejection devices and printheads.
This patent grant is currently assigned to STMICROELECTRONICS, INC., STMICROELECTRONICS S.R.L.. The grantee listed for this patent is STMICROELECTRONICS, INC., STMICROELECTRONICS S.R.L.. Invention is credited to Simon Dodd, Marco Ferrera, Domenico Giusti, Carlo Luigi Prelini.
United States Patent |
11,084,283 |
Giusti , et al. |
August 10, 2021 |
Methods of forming and using fluid ejection devices and
printheads
Abstract
Ejection device for fluid, comprising a solid body including:
first semiconductor body including a chamber for containing the
fluid, an ejection nozzle in fluid connection with the chamber, and
an actuator operatively connected to the chamber to generate, in
use, one or more pressure waves in the fluid such as to cause
ejection of the fluid from the ejection nozzle; and a second
semiconductor body including a channel for feeding the fluid to the
chamber, coupled to the first semiconductor body, in such a way
that the channel is in fluid connection with the chamber. The
second semiconductor body integrates a damping cavity over which
extends a damping membrane, the damping cavity and the damping
membrane extending laterally to the channel for feeding the
fluid.
Inventors: |
Giusti; Domenico (Caponago,
IT), Ferrera; Marco (Concorezzo, IT),
Prelini; Carlo Luigi (Seveso, IT), Dodd; Simon
(West Linn, OR) |
Applicant: |
Name |
City |
State |
Country |
Type |
STMICROELECTRONICS S.R.L.
STMICROELECTRONICS, INC. |
Agrate Brianza
Coppell |
N/A
TX |
IT
US |
|
|
Assignee: |
STMICROELECTRONICS S.R.L.
(Agrate Brianza, IT)
STMICROELECTRONICS, INC. (Coppell, TX)
|
Family
ID: |
1000005729648 |
Appl.
No.: |
16/676,070 |
Filed: |
November 6, 2019 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20200070511 A1 |
Mar 5, 2020 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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15884186 |
Jan 30, 2018 |
10493758 |
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Foreign Application Priority Data
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Mar 28, 2017 [IT] |
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102017000034134 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B41J
2/1631 (20130101); B41J 2/055 (20130101); B41J
2/1626 (20130101); B41J 2/1629 (20130101); B41J
2/18 (20130101); B41J 2/1628 (20130101); B41J
2/1623 (20130101); B41J 2/14233 (20130101); B41J
2/14 (20130101); B05B 1/02 (20130101); B41J
2/161 (20130101); B41J 2002/14346 (20130101); B41J
2202/12 (20130101); B41J 2002/14403 (20130101); B41J
2002/14419 (20130101) |
Current International
Class: |
B41J
2/14 (20060101); B41J 2/18 (20060101); B41J
2/16 (20060101); B41J 2/055 (20060101); B05B
1/02 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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101125480 |
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Feb 2008 |
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CN |
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102344111 |
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Feb 2012 |
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CN |
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105711258 |
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Jun 2016 |
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CN |
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2010-188547 |
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Sep 2010 |
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JP |
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Primary Examiner: Thies; Bradley W
Attorney, Agent or Firm: Seed Intellectual Property Law
Group LLP
Claims
The invention claimed is:
1. A method for manufacturing a fluid ejection device, the method
comprising: forming a chamber configured to receive a fluid, the
chamber including a first membrane at a first surface of the
chamber; forming an ejection nozzle in fluidic connection with the
chamber; forming a damping membrane; and forming a reservoir
chamber, wherein the first membrane is configured to cause fluid in
the chamber to be ejected through the ejection nozzle, wherein the
reservoir chamber is fluidically coupled to the chamber by a fluid
path and configured to provide the fluid to the chamber, and
wherein the damping membrane faces the reservoir chamber and is
configured to dampen the fluid in the reservoir chamber, wherein
the chamber, the first membrane, and the damping membrane are
arranged stacked relative to one another.
2. The method according to claim 1, wherein the damping membrane is
configured to dampen the fluid in the chamber.
3. The method according to claim 1, wherein forming the damping
membrane comprises forming a closed cavity in the monolithic body,
the damping membrane facing the closed cavity.
4. The method according to claim 3, further comprising forming a
filter in in the monolithic body that forms a portion of the fluid
path.
5. The method according to claim 4, wherein the closed cavity is
formed before the filter is formed.
6. The method according to claim 3, wherein the monolithic body is
made of semiconductor material.
7. The method according to claim 3, wherein the monolithic body is
one of: glass, germanium, or silicon.
8. A method, comprising: receiving fluid from a reservoir chamber
through an inlet and providing the fluid to a chamber; causing a
first deflection of a first membrane in a first direction that
causes at least a drop of the fluid to exit through a nozzle hole;
causing a second deflection of the first membrane in a second
direction, the second direction being opposite to the first
direction; and dampening pressure waves in the fluid in the chamber
using a second membrane in the reservoir chamber, wherein the first
membrane is stacked relative to the second membrane such that the
first membrane and the second membrane overlap in the first and
second directions.
9. The method according to claim 8, wherein dampening pressure
waves in the fluid in the chamber comprises deflecting the second
membrane into a cavity.
10. The method according to claim 9, wherein the cavity is adjacent
to a fluid path that couples the chamber to the reservoir
chamber.
11. The method according to claim 8, wherein prior to receiving the
fluid, filling the reservoir chamber with the fluid.
12. The method according to claim 8, wherein receiving the fluid
includes filtering the fluid.
13. The method according to claim 8, wherein the first deflection
of the first membrane in the first direction reduces a volume of
the chamber, and wherein the second deflection of the first
membrane in the second direction increases the volume of the
chamber.
14. The method according to claim 13, wherein the first deflection
is a same amount as the second deflection.
15. A method, comprising: filtering a fluid received from a
reservoir chamber; storing the filtered fluid in a chamber;
deflecting a first membrane in a first direction to cause one or
more drops of the fluid to be expelled through a nozzle hole; and
deflecting the first membrane in a second direction, the second
direction being opposite to the first direction, wherein a second
membrane in the reservoir chamber dampens pressure waves in the
fluid in the reservoir chamber and the chamber, wherein the first
membrane is stacked relative to the second membrane such that the
first and second membranes overlap in the first and second
directions.
16. The method according to claim 15, wherein the second membrane
is located in the reservoir chamber.
17. The method according to claim 15, wherein the second membrane
is located in a same monolithic body that is used to filter the
fluid.
18. The method according to claim 15, wherein the second membrane
has a main surface that faces a main surface of the first
membrane.
19. The method according to claim 15, wherein the first deflection
of the membrane in the first direction reduces a volume of the
chamber, and wherein the second deflection of the membrane in the
second direction increases the volume of the chamber.
20. The method according to claim 15, wherein the first deflection
is a same amount as the second deflection.
Description
BACKGROUND
Technical Field
The present disclosure relates to a fluid ejection device with an
element for reducing cross disturbances ("crosstalk"), to a
printhead including the ejection device, to a printer including the
printhead and to a method for manufacturing the fluid ejection
device.
Description of the Related Art
In the current state of the art multiple types of fluid ejection
device are known, in particular "inkjet" devices for printing
applications.
Similar devices, with suitable modifications, can also be used for
the emission of various types of fluids, for example in the sphere
of applications in the biological or biomedical field, for local
ejection of biological material (e.g., DNA) during the
manufacturing of sensors for biological analyses.
An example of an ejector element with piezoelectric actuation of
known type is shown in FIG. 1 and indicated with the reference
number 1. A plurality of ejector elements 1 form, at least in part,
a printing device ("printhead").
With reference to FIG. 1, a first wafer or plate 2, e.g., of
semiconductor material or metal, is processed to form one or more
piezoelectric actuators 3 on it, capable of causing a deflection of
a membrane 7 extending partially suspended above one or more
chambers 10, suitable for temporary containment of a fluid 6 to be
expelled during use.
A second wafer or plate 4, of semiconductor material, is processed
so as to form one or more containment chambers 5 for the
piezoelectric actuators 3, so as to isolate, in use, the
piezoelectric actuators 3 from the fluid 6 to be expelled.
A third wafer or plate 12, of semiconductor material, configured
for being arranged above the second plate 4, is processed so as to
form expulsion holes 13 for the fluid 6 ("outlet" holes).
A fourth wafer or plate 8, of semiconductor material, configured to
be arranged below the second plate 4, is processed so as to form
one or more input holes ("inlet" holes) 9a for the fluid 6 into the
chamber 10, and one or more recirculating holes 9b for the fluid 6,
which form a route for the recirculation of the fluid 6 not
ejected.
Afterwards, plates 2, 4, 8 and 12 are assembled together by means
of soldering interface regions ("bonding regions") or gluing
interface regions ("gluing regions") or adhesive interface regions
("adhesive regions"), or Au frit, or glass frit, or by means of
polymeric bonding. These regions are generically indicated in FIG.
1 by the reference number 15.
In addition, the printing device 1 is equipped with a collector
(better known as a "manifold") 16 which has the function of feeding
the fluid 6 into the chamber 10. The manifold 16 comprises a feed
channel 17, operatively coupled to a tank ("reservoir"), not shown,
from which it receives, during use, the fluid 6 which is fed to the
chamber 10 via the inlet hole 9a. Furthermore, the manifold 16
comprises a recirculating channel 18 by means of which the fluid 6
that was not emitted through the expulsion hole 13 is fed back into
the reservoir. The reservoir is shared between a plurality of
printing devices of the type shown in FIG. 1.
To allow the ejection of the fluid 6 through the outlet hole 13,
the piezoelectric actuator 3 is controlled in such a way as to
generate a deflection of the membrane 7 towards the inner part of
the chamber 10. This deflection causes a movement of the fluid 6
through the outlet hole 13 for the controlled expulsion of a drop
of fluid towards the outer part of the printing device 1. However,
the pressure wave applied to the fluid 6 is further propagated,
both along the recirculating channel 18, and along the feed channel
17, returning towards the manifold 16 and, from here, towards the
reservoir. Pressure waves are thus generated, during use, towards
the reservoir, and within the fluid contained in the reservoir
itself, which causes a disturbance during the operative steps
(loading of the fluid towards chamber 10 and recirculation of the
fluid towards the reservoir) of other printing devices sharing the
same reservoir. It is common to refer to this type of disturbances
as "crosstalk."
The manifold 16 is structured so as to minimize the propagation of
pressure disturbances between chambers 10 of mutually adjacent
ejector elements 1.
To this end, the manifold 16 has a first attenuation membrane 19a,
suspended over a first cavity 20a, directly facing the inlet hole
9a; and a second attenuation membrane 19b, suspended over a second
cavity 20b, directly facing the recirculation hole 9b.
In use, the first and the second membranes 19a, 19b are deflected
in response to the pressure waves which are generated in fluid 6
during the oscillation of membrane 7, and which propagate from here
towards the underlying reservoir. In this way, the first and second
membranes 19a, 19b, by absorbing at least in part the pressure
force, reduce the impact of said force both on the internal walls
of the fourth plate 8, and on the liquid contained in the
reservoir, limiting its propagation towards the other ejector
elements 1 of the printing device. Therefore, the presence of
membranes 19a, 19b cooperates in ensuring that each drop ejected by
an ejector element 1 is not influenced by the operation of other
ejector elements 1. The manifold 16 also comprises an inlet filter
21a located at the entrance of the feed channel 17 and configured
to trap undesired particulates, and a recirculation filter 21b
located at the outlet of the recirculation channel 18. Filters are
typically made of stainless steel or a polymer and are mechanically
attached or glued to the printhead. The filters can be very
expensive and the mechanical assembly further adds cost and
complexity to the printhead.
Moreover, the assembling process of the manifold 16 requires high
accuracy and precision in aligning the feed channel 17 with the
inlet hole 9a and in aligning the recirculation channel 18 with the
recirculation hole 9b, ensuring that there are no air leaks which
would irremediably compromise the functionality of the ejector
element. This process is, therefore, onerous and subject to
manufacturing errors.
BRIEF SUMMARY
One or more embodiments are directed to a fluid ejection device
having an element for reducing crossing disturbances ("crosstalk"),
a printhead including the ejection device, a printer including the
printhead and a method for manufacturing the fluid ejection device.
Other embodiments are directed to a manufacturing process for a
fluid ejection device based on piezoelectric technology with an
integrated crosstalk-attenuation element. Furthermore, the present
disclosure relates to the application of said fluid ejection device
to a printhead and to a printer including said printhead.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
For a better understanding of the present disclosure, preferred
embodiments thereof are now described, purely by way of
non-limiting example, with reference to the attached drawings, in
which:
FIG. 1 shows a printing device with piezoelectric actuation with a
collector region according to an embodiment of known type;
FIG. 2 shows in perspective and from above a printhead with
piezoelectric actuation with an integrated damper according to an
embodiment of the present disclosure;
FIGS. 3-16 show, in a cross-section view, manufacturing steps of a
fluid ejection element according to an aspect of the present
disclosure, as an integrated acoustic damper according to one
embodiment;
FIG. 17 shows a printhead comprising the ejection device of FIG.
16;
FIG. 18 shows a block diagram of a printer including the printhead
shown in FIG. 17; and
FIG. 19 shows a fluid ejection device according to a further
embodiment of the present disclosure.
DETAILED DESCRIPTION
FIG. 2 shows, in perspective and in a triaxial reference system X,
Y, Z, a portion of a printing device 200 including a plurality of
fluid ejection elements 150 according to an aspect of the present
disclosure. Each fluid ejection device 150 includes an integrated
damper 201 made up of a respective membrane extending over a
respective buried cavity 40. FIG. 2 shows a plurality of buried
cavities 40, extending, in plan view over plane XY, sidelong with
inlet holes 123 of the fluid ejection devices 150. Inlet holes 123
are capable of being coupled to a manifold and, therefore, to a
fluid reservoir, to receive the fluid that is to be ejected during
use. Thus, a group of fluid ejection devices 150, aligned in the
same direction parallel to axis Y, shares the same integrated
attenuator 201. Each buried cavity 40 is fluidically connected to
the external environment by means of a respective channel 40' which
extends as a prolongation of cavity 40 along axis Y. The opening of
channel 40' is carried out during a cutting step (separation or
"dicing") of the printing device 200.
The manufacturing process and the mode of operation of each fluid
ejection device 150 with the integrated attenuator 201 are
described hereafter.
FIGS. 3-12 show, in transverse section view, steps of processing a
"wafer" of semiconductor material 30 for forming the buried cavity
40, and, thus, the integrated attenuator 201 according to the
present disclosure.
According to further embodiments, not disclosed in detail but
apparent to skilled person, the wafer 30 may be, at least in part,
of a material which is not a semiconductor, e.g., glass or
germanium.
With reference to FIG. 3, the semiconductor wafer 30 is shown,
including a substrate 31, in particular of silicon (e.g., single
crystal), in an initial step of the manufacturing process which
provides for the formation of a plurality of trenches 32 and
32a.
In particular, as better described below, the trenches 32 are
formed at regions of the substrate 31 in which it is desired to
form the buried cavity 40 for the integrated damper (shown in FIG.
7 at the end of the steps of its formation).
The trenches 32a are formed in regions of the substrate 31 in which
it is desired to form an inlet region for a fluid to be ejected by
the ejection device 150. The fluid inlet region includes, as better
described in the following, the inlet hole 123 (capable of being
coupled to a manifold and to a fluid reservoir) and an integrated
filter for filtering any undesired particulate present in the
fluid.
With reference to FIG. 3, above an upper surface 31a of the
substrate 31, a mask 33 for photolithography is formed, for example
of photoresist film.
Mask 33, in top view on plane XY, has a lattice conformation, for
example honeycomb; FIG. 3 shows portions 33a of mask 33, connected
to form said lattice, after the lithography and chemical etching
steps to form trenches 32, 32a.
Trenches 32, 32a, having their principal extension along axis Z,
are etched by an anisotropic chemical etching on substrate 31,
starting from a front side of substrate 31. Considering, for
example, a substrate 31 of a thickness of about 100-500 .mu.m,
trenches 32, 32a have a depth of about 80-400 .mu.m. In general,
the trenches extend into the substrate 31 as far as a distance,
from a rear side of the substrate 31 (opposite to the front side),
of about 20-100 .mu.m.
Subsequently, FIG. 4, still with mask 33 positioned over the upper
surface 31a of the substrate 31, a deposition of silicon dioxide
(SiO.sub.2) or other dielectric material (such as, for example,
silicon oxynitride or nitride) is carried out, in order to form
spacers 36 on the lateral inside walls of trenches 32 and 32a. It
is noted that any dielectric material formed on the bottom of the
trenches 32, 32a is removed by anisotropic etching.
Subsequently, FIG. 5, a step of isotropic chemical etching is
carried out, for example with the etching chemistry TMAH
(tetramethylammonium hydroxide), so as to form a first and a second
open cavity 38, 39, in fluidic communication with trenches 32, 32a
respectively. In particular, the isotropic chemical etching erodes
the portion of the substrate 31 below the trenches 32, 32a, both in
the direction of depth Z (direction of principal extension of
trenches 32, 32a) and in a lateral direction, transverse to said
vertical direction (i.e., on plane XY). The extension on plane XY
of the open cavities 38, 39 substantially corresponds to the
extension, still on plane XY, of mask 33 previously formed over the
substrate 31.
As shown in FIG. 6, mask 33 is removed from the upper surface 31a
of the substrate 31 and the dielectric material 36 previously
deposited on the walls of the trenches 32, 32a is also removed, for
example by wet etching ("wet etching").
As shown in FIG. 7, a step of epitaxial growth of monocrystalline
or polycrystalline silicon is carried out, preferably in a
deoxidizing environment (typically, in an atmosphere with a high
concentration of hydrogen, preferably in trichlorosilane,
SiHCl.sub.3), closing off trenches 32, 32a at the top. Optionally,
a heat treatment ("annealing") step is performed, for example in a
nitrogen (N.sub.2) atmosphere, in particular at a temperature of
about 1200.degree. C.; the annealing step causes a migration of
silicon atoms, which tend to move to lower energy positions thus
completing the formation of the buried cavity 40 (at the region in
which the trenches 32 extend) and of a buried cavity 41 (at the
region in which the trenches 32a extend).
The buried cavities 40 and 41, at this step of manufacturing, are
completely isolated from the external environment and contained
within substrate 31 itself; above cavities 40 and 41 there extends
a first surface layer 42, compact and uniform, consisting partly of
epitaxially grown mono- or polycrystalline atoms and partly of
silicon atoms which migrated during the previous annealing step,
and having a thickness, for example, of between 1 .mu.m and 300
.mu.m.
Below the buried cavity 40 there extends a portion of substrate 31
which forms a membrane 35 suspended over the buried cavity 40. The
membrane 35 has a thickness, measured along the direction of axis
Z, of between 1 .mu.m and 50 .mu.m, in particular equal to 5
.mu.m.
The process continues with steps for the formation of an integrated
antiparticulate filter. To this end, over an upper surface 42a of
the first surface layer 42, a mask of suitable shape (as better
clarified below) is formed, utilized for performing a step of
selective oxidization. In this way the structure of FIG. 8 is
obtained, wherein on the upper surface 42a of the first surface
layer 42 an etching mask 44 formed of silicon dioxide or other
dielectric material is present. In particular, the etching mask 44
has a lattice structure defining apertures 44a at the buried cavity
41. Apertures 44a are spaced at a regular distance, of between 0.5
.mu.m and 50 .mu.m along direction X. The same spacing is present
along direction Y. Alternatively, apertures 44a can have a
different extension along axes X and Y. As said before, etching
mask 44 has the aforesaid apertures 44a solely at the second buried
cavity 41; in the remaining part of its extension, etching mask 44
does not have other empty spaces and is, therefore, continuous.
As shown in FIG. 9, the process continues with a step of epitaxial
growth of monocrystalline or polycrystalline silicon, following
which a second surface layer 45 is formed above the first surface
layer 42. Consequently, etching mask 44 results interposed between
the first and the second surface layer 42, 45 respectively.
As shown in FIG. 10, on top of an upper surface 45a of the second
surface layer 45, regions of inlet mask 43 and regions of edge mask
43' are formed.
The regions of edge mask 43' are suitable for delimiting a portion
of the second surface layer 45 that, in subsequent steps, will
operate as a containment chamber for a piezoelectric actuator. The
regions of inlet mask 43 are suitable for delimiting a surface
portion 47a of the second surface layer 45 in correspondence to
which, in subsequent steps, part of the fluid inlet channel will be
formed.
A photolithographic mask 46 is formed, over the upper surface 45a
of the second surface layer 45, which leaves the surface portion
47a adjacent to the apertures 44a of the etching mask 44 uncovered
(i.e., aligned with the apertures 44a along axis Z).
A deep etching step of anisotropic type on the silicon is carried
out, FIG. 11, and with an etching depth such that it involves the
entire thickness of the second surface layer 45 and that of the
first surface layer 42. In particular, the etching removes the
portions of the first surface layer 42 which are not protected by
the mask 44. The etching mask 44 in fact works as a screen for the
etching and ensures that the underlying portions of silicon remain
substantially intact, in fact replicating the lattice structure and
conformation, on plan, of the etching mask 44 itself, and
consequently forming a filter element 49. Thus, above the second
buried cavity 41, the filter element 49 of the type integrated into
the silicon is formed.
The filter element 49 is thus made up of a lattice structure with
vertical extension (with a height substantially equal to the
thickness of the first surface layer 42), defining on its interior
a plurality of apertures 50, in order to enable the passage of the
fluid through them and to trap undesired particles (having
dimensions not compatible with the dimensions of the apertures 50);
between adjacent apertures 50 there are vertical walls or
plates.
In particular, the deep etching on the silicon through the
lithographic mask 46 leads to the creation of a duct 48a which
crosses the second surface layer 45 through its entire thickness
and reaches the second buried cavity 41 through the filter element
49 (and vice versa). The filter element 49 is located so as to be
separated from the upper surface 45a of the second surface layer 45
by the thickness of the second surface layer 45 itself, and
interposed between duct 48a and buried cavity 41.
The etch step which leads to the formation of duct 48a in fluidic
communication with the second buried cavity 41 automatically leads
and at the same time to the formation of filter element 49 which is
connected to the same access duct 48a, due to the previous
formation of the etching mask 44 in an appropriate position and
configuration; in particular, the filter element 49 is formed
directly over the second buried cavity 41, which is integrated into
the semiconductor material of which the first surface layer 42 is
formed.
The process ends, FIG. 12, with a removing step of the
photolithographic mask 46, and a subsequent etch, indicated by the
arrows 52, for the purpose of completing the formation of the wafer
30 forming a housing 58 for the piezoelectric actuator (an actuator
80 is described with reference to FIG. 13) and a housing for
electrical contacts 59, as is better explained below.
At the end of these removal steps, there is obtained a
micromechanical structure including the membrane 35 suspended over
the buried cavity 40, whose function is as an integrated damper to
reduce the crosstalk; and the buried cavity 41 communicating with
duct 48a through the filter element 49. As it has been said, this
filter element 49 is capable of trapping particles, impurities
and/or contaminants coming from the external reservoir (not shown
here) during the feeding of the fluid to be ejected.
Both buried cavities 40, 41 and the filter element 49 are
integrated into the same monolithic body (which, according to an
aspect of the present disclosure, is of semiconductor
material).
It should furthermore be emphasized that: the design or pattern of
the etching mask 44, once the process is completed, determines the
corresponding filtering pattern of the filter element 49; and the
position of the etching mask 44 itself with respect to the second
buried cavity 41 determines the corresponding position of the
filter element 49, and, therefore, its function with respect to the
filtering of impurities coming from outside, through the cavity and
into the containment chamber 130.
The process continues with the manufacturing steps to complete the
formation of the fluid ejection device.
With reference to FIG. 13, a description is now given of
manufacturing steps of an actuator element 80, here of
piezoelectric type. The actuator element 80 is manufactured in a
known manner. Briefly, a substrate 81 is provided (e.g., made of
semiconductor material as silicon). However, the substrate 81 can
be of a different material, like germanium, or any other suitable
material. On this substrate 81, a layer of membrane 82, of flexible
material, is formed. In further embodiments, the membrane can be
formed from various types of materials typically used for MEMS
devices, for example silicon dioxide (SiO.sub.2) or silicon nitride
(SiN), of a thickness, for example, between 0.5 and 10 .mu.m, or it
can be formed from a stack of silicon dioxide, silicon, silicon
nitride (SiO.sub.2--Si--SiN) in various combinations.
The process continues with the formation, on the membrane layer 82,
of a lower electrode 83 (for example, made of a layer of titanium
dioxide, TiO.sub.2, with a thickness of between 5 and 50 nm, onto
which is deposited a layer of platinum, Pt, with a thickness, e.g.,
of between 30 and 300 nm).
The process continues with the deposition of a piezoelectric layer
over the lower electrode 83, depositing a layer of
lead-zirconium-titanium trioxide (Pb--Zr--TiO.sub.3, or PZT) having
a thickness, for example, of between 0.5 and 3.0 .mu.m (which,
after subsequent shaping steps, will form the piezoelectric region
84); subsequently, a second layer of conductive material, e.g.,
platinum (Pt) or iridium (Ir) or iridium dioxide (IrO.sub.2) or
titanium-tungsten (TiW) or ruthenium (Ru), having a thickness, for
example of between 30 and 300 nm, is deposited to form an upper
electrode 85.
The electrode and piezoelectric layers undergo lithography and
etching steps, to model them according to a desired pattern thus
forming the lower electrode 83, the piezoelectric region 84 and the
upper electrode 85. The set of these three elements constitutes a
piezoelectric actuator.
One or more passivation layers 86 are deposited on the lower
electrode 83, the piezoelectric region 84 and the upper electrode
85. The passivation layers include dielectric materials used for
electrical insulation of the electrodes, for example, layers of
silicon dioxide (SiO.sub.2) or silicon nitride (SiN) or aluminum
oxide (Al.sub.2O.sub.3), individually or in superimposed stacks, of
a thickness, for example, between 10 nm and 1000 nm. The
passivation layers are attached in correspondence to selective
regions, to create access trenches to the lower electrode 83 and
the upper electrode 85. The process continues with a step of
deposition of conductive material, such as metal (e.g., aluminum,
Al, or gold, Au, possibly together with barrier and adhesion layers
such as titanium, Ti, titanium-tungsten, TiW, titanium nitride,
TiN, tantalum, Ta, or tantalum nitride, TaN), inside the trenches
thus created and over the passivation layers 86. A subsequent
modelling step ("patterning") allows to form conductive tracks 87,
88 which enable selective access to the upper electrode 85 and the
lower electrode 83, to polarize them electrically during use. It is
also possible to form further passivation layers (e.g., of silicon
dioxide, SiO.sub.2, or silicon nitride, SiN) to protect the
conductive tracks 87, 88. Conductive pads 92 are also formed
laterally to the piezoelectric actuator, and are electrically
coupled to the conductive tracks 87, 88.
The membrane 82 is selectively etched in correspondence to a region
thereof which extends laterally, and at a distance, from the
piezoelectric region 84, to expose a surface region of the
underlying actuator substrate 81. A through hole 89 is thus formed
through the membrane layer 82 which makes it possible, in later
manufacturing steps, to generate a fluid connection with the access
duct 48a and, via the latter, with cavity 41 in wafer 30.
Substrate 81 of the actuator element 80 is "etched" so as to form a
cavity 93 on the opposite side with respect to the side which
houses the actuator element 80. Through cavity 93, the layer of
silicon dioxide which forms membrane 82, is exposed. This step
allows to free membrane 82, making it suspended.
With reference to FIG. 14, the semiconductor wafer 30 and the
actuator element 80 thus manufactured are coupled together (e.g.,
using the "wafer-to-wafer bonding" technique) in such a way that
the housing 58 of the semiconductor wafer 30 completely contains
the actuator element 80 and in such a way that the hole 89 made
through the membrane 82 is aligned, and in fluidic connection, with
the access duct 48a formed through the substrate 31 of the
semiconductor wafer 30.
With reference to FIG. 15, processing steps are described for a
wafer 100 for forming the outlet hole of the fluid ejection
element. The processing steps provide, in brief, for arranging a
substrate 111 of semiconductor material (for example, silicon).
This substrate 111 has a first and a second surface 111a, 111b,
which are subjected to a thermal oxidization process which leads to
the formation of an anti-wetting layer 112 and a lower oxide layer
110.
On the surface of the anti-wetting layer 112 a first nozzle layer
113 is formed, for example of epitaxially grown polysilicon, having
a thickness, for example, of between 10 and 75 .mu.m.
The first nozzle layer 113 can be of a material other than
polysilicon, for example it can be of silicon or another material,
provided that it can be selectively removed with respect to the
material of which the anti-wetting layer 112 is formed.
Therefore, by means of successive steps of lithography and etching,
a nozzle hole 121 is formed through the first nozzle layer 113,
until a surface region of the anti-wetting layer 112 is
exposed.
The etching is carried out using a chemical etching capable of
selectively removing the material of which the first nozzle layer
113 is made (here, polysilicon), but not the material of which the
anti-wetting layer 112 is made (here, silicon dioxide, SiO.sub.2).
The etching profile for the first nozzle layer 113 can be
controlled by choosing an etching technology and a chemical etching
in order to achieve the desired result, such as, for example,
dry-type etchings (RIE or DRIE) with semiconductor industry
standard chemicals for etching silicon (SF.sub.6, HBr, etc.) to
obtain a nozzle hole 121 with strongly vertical lateral walls.
In the subsequent steps of manufacturing, if necessary, both the
first nozzle layer 113 and the nozzle hole 121 undergo a cleaning
process, aimed at removing undesired polymeric layers which can be
formed during the preceding etch step. This cleaning process is
carried out by removing in oxidizing environments at high
temperature (>250.degree. C.) and/or in aggressive solvents.
A step of thermal oxidization of the outlet wafer 100, for example
at a temperature of between 800.degree. C. and 1100.degree. C., is
carried out, to form a layer of thermal oxide 114 over the first
nozzle layer 113. This step has the function of allowing the
formation of a thin layer of thermal oxide 114 with low surface
roughness. Instead of using thermal oxidization, the above oxide
can be deposited, wholly or in part, for example with CVD
("Chemical Vapor Deposition") techniques.
The thermal oxide layer 114 extends over the upper face of the
outlet wafer 100 and inside the nozzle hole 121, covering its
lateral walls. The thickness of the thermal oxide layer 114 is, for
example, between 0.2 .mu.m and 2 .mu.m.
Above the thermal oxide layer 114 a second nozzle layer 115 is
formed, for example in polysilicon. The second nozzle layer 115 has
a final thickness, for example, of between 80 and 150 .mu.m. The
second nozzle layer 115 is, for example, epitaxially grown above
the thermal oxide layer 114 and inside the nozzle hole 121, until
it reaches a thickness greater than the desired thickness (for
example about 3-5 .mu.m greater); subsequently, it is subjected to
a step of CMP ("Chemical Mechanical Polishing") to reduce its
thickness and obtain an exposed upper surface with low
roughness.
The process continues with the formation of a feed channel 120 for
the nozzle and for removing the polysilicon which, in the previous
step, filled the nozzle hole 121. To this end, use is made of
masking and etching techniques which are known. The etching is
carried out with a chemical etching that is suitable for removing
the polysilicon of which the second nozzle layer 115 is formed, but
not the silicon dioxide of the thermal oxide layer 114. The etching
proceeds until the complete removal of the polysilicon, which
extends inside the nozzle hole 121, is achieved, forming the feed
channel 120 through the second nozzle layer 115 in fluid
communication with the nozzle hole 121.
With reference to FIG. 16, the wafer 100, the actuator element 80
and the wafer 300 are coupled to each other by means of the
"wafer-to-wafer bonding" technique using adhesive materials for the
bonding, which may for example be polymeric or metallic or vitreous
materials.
The process continues with processing steps the wafer 100, to
complete the formation of a nozzle hole 121. To this end, the
process continues with a removal step of the lower oxide layer 110
and the base layer 111. This step can be carried out by grinding
the lower oxide layer 110 and part of the base layer 111, or by a
chemical etching or by a combination of these two processes.
Following the process of grinding and/or chemical etching, in
correspondence to the nozzle hole 121 and the upper surface of the
first nozzle layer 113, the upper oxide layer 112 is removed,
completing the formation of the nozzle. The removal is performed,
for example, using a dry type etching, with a standard chemical
etching for semiconductor technology.
According to one aspect of the present disclosure, layer 112 is
removed above layer 113 in correspondence to the ink output
nozzles.
The description given is valid, similarly, also in the event that
on the upper oxide layer 112 there are also one or more
anti-wetting layers. In this event, however, the removing step of
the base layer 111 or the upper oxide layer 112 stops at the
anti-wetting layer, which is not removed, or it is removed along
the walls of the nozzle hole 121 if it is present there.
The processing of the wafer 30 is completed, by etching selective
portions of the substrate 31 in correspondence to the cavity 41. In
this way, cavity 41 is in fluidic communication with the exterior.
Note that duct 48a extends along axis Z with an offset with respect
to the inlet hole 123. In this way, cavity 41 collects part of the
fluid 6 before it is introduced to duct 48a, cooperating with
membrane 35 to reduce crosstalk. Cavity 41 performs, in part, the
functions of the manifold according to the known art. In
particular, cavity 41 has the function of containing the filtered
particles; furthermore, it ensures fluidic continuity between the
reservoir and duct 48a.
A step of partial cutting ("partial sawing") of the wafer, housing
the actuator element 80, along the cutting line 125 shown in FIG.
16, makes it possible to remove an edge portion of said wafer in
correspondence to the conductive pads 92, so as to make them
accessible from the outside for a subsequent wire bonding
operation.
In this way, the fluid ejector element 150 is obtained provided
with attenuator and integrated filter in silicon.
FIG. 17 schematically shows a printhead 250 comprising a plurality
of fluid ejecting elements 150 formed as previously described.
The printhead 250 can be used not only for inkjet printing, but
also for applications such as the high precision deposition of
liquid solutions containing, for example, organic material, or
generally in the sphere of depositing techniques of "inkjet
printing" type, for the selective deposition of materials in a
liquid state.
The printhead 250 furthermore comprises a reservoir 251, located
below the fluid ejection elements 150, suitable for containing in
its own internal housing 252 the fluid 6 (for example ink).
Between the reservoir 251 and the fluid ejection elements 150 there
extends a manifold 260 having, as is known, the function of
interface between the reservoir 251 and the fluid ejection elements
150. In particular, the manifold 260 includes a plurality of feed
channels 256 which fluidly connect the reservoir 255 with a
respective inlet hole 123 of the fluid ejection elements 150.
The printhead 250 can be incorporated into any printer 300 of known
type, for example of the type shown schematically in FIG. 18.
The printer 300 of FIG. 18 comprises a microprocessor 310, a memory
320 connected to the microprocessor 310, a printhead 250 according
to the present disclosure, and a motor 330 for moving the printhead
250. The microprocessor 310 is connected to the printhead 250 and
to the motor 330, and it is configured for coordinating the
movement of the printhead 250 (effected by operating the motor 330)
and the ejection of the liquid (for example, ink) from the
printhead 250. The operation of ejecting the liquid is effected by
controlling the operation of the actuator 91 of each fluid ejection
element 150.
In use, ejector element 150 operates according to the following
steps.
In a first step, the chamber 130 is filled by the fluid 6 which it
is desired to eject. This step of loading the fluid 6 is executed
through the access duct 48a, which receives the fluid 6 via the
feed channel 123, from the reservoir 251 through the cavity 41 and
the filter element 49.
In a second step, the piezoelectric actuator 91 is controlled in
such a way as to generate a deflection of the membrane 82 towards
the inner part of chamber 130. This deflection causes a movement of
the fluid 6 through the feed channel 120 and the nozzle hole 121
and generates the controlled expulsion of a drop of fluid 6 towards
the outside of the ejector element.
In a third step, the piezoelectric actuator 91 is controlled in
such a way as to generate a deflection of membrane 82 in the
opposite direction from the preceding step, so as to increase the
volume in the chamber 130, calling further fluid 6 towards the
chamber 130 through the access duct 48a. The chamber 130,
therefore, is recharged with fluid 6. It is possible to proceed
cyclically by operating the piezoelectric actuator 91 to expel
further drops of fluid. In practice, the second and the third step
are repeated until the end of the printing process.
During the steps of loading the fluid 6 into the chamber 130 and
expelling the fluid 6 through the nozzle hole 121, pressure waves
in the fluid 6 are generated, which spread in the direction of the
reservoir 251 and which, consequently, can interfere with the
normal process of loading the fluid 6 into the chambers 130 of the
ejection elements 150 belonging to the same printhead 250.
According to the present disclosure, the membrane 35, having the
function of integrated damper, operates as an absorption element
for the pressure waves directed towards the inlet hole 123 of each
ejection element 150. In fact, the membrane 35, suspended over the
cavity 40, is arranged, in an embodiment of the present disclosure,
at least in part upstream the access duct 48a and cavity 41 (in
particular, coplanar to the inlet hole 123). More specifically, the
membrane 35 extends laterally to the inlet hole 123 and cavity 41.
In this way, the pressure waves directed towards the inlet hole 123
are damped before they enter the access duct 48a.
Thus for each individual fluid ejection element 150, a compensation
effect for the pressure waves generated by the other ejection
elements 150 belonging to the same printhead 250 is obtained, as
well as a significant reduction in crosstalk.
From an examination of the characteristics of the disclosure
achieved according to the present disclosure, the advantages that
can be obtained from it are evident.
In particular, with reference to the first cavity 40 and to
membrane 35, the integration of the dumping element into substrate
31 makes it possible to reduce manufacturing costs, prevent air
leaks to the outside of the printing device and make the
manufacturing process more accurate and faster.
Finally, it is clear that modifications and variants may be made to
what is here described and illustrated without for this reason
departing from the protective scope of the present disclosure.
In particular, the embodiment of the fluid ejection element
previously described and illustrated in the drawings comprises an
inlet channel (made up of inlet hole 123, cavity 41 and duct 48a)
which enable a flow of a liquid to be expelled which flows from
reservoir 251, through manifold 260, towards the inner chamber 130.
There is no expectation, in this case, for a recirculating channel
to allow the fluid that has not been expelled from chamber 130 to
return towards the manifold 260 and from here into the reservoir
251. FIG. 19 illustrates this further embodiment, in which there is
a recirculating channel 97 which extends laterally to the cavity 40
in correspondence to a side of said cavity opposite to the side on
which the inlet channel extends.
Furthermore, even if the present disclosure has been disclosed
making explicit reference to various semiconductor bodies coupled
to one another (e.g., wafers 30 and 100 and actuator element 80),
it is anyway possible to process a single piece of solid material
(e.g., semiconductor), integrating in it the fluid containing
chamber 130, the actuator element 80, and the damper (i.e., the
membrane 35 suspended over the cavity 40).
The various embodiments described above can be combined to provide
further embodiments. These and other changes can be made to the
embodiments in light of the above-detailed description. In general,
in the following claims, the terms used should not be construed to
limit the claims to the specific embodiments disclosed in the
specification and the claims, but should be construed to include
all possible embodiments along with the full scope of equivalents
to which such claims are entitled. Accordingly, the claims are not
limited by the disclosure.
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